Mercury capillary interrupter



Aug. 22, JAMES E. WEBB 3 ADMINISTRATOR OF TI-IE NATIONAL AERoNAuTIcs ANDsPAcE ADMINISTRATION MERCURY CAPILLARY INTERRUPTER Filed Feb. 11, 1965I? f-E l5 -I:f 2 I5 FIG. I

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POWER 49 SUPPLY IIIIIEIIIoR, FIG. 3 CLARENCE H.HECKLER ATTORNEYS UnitedStates Patent 3,337,790 MERCURY CAPILLARY INTERRUPTER James E. Webb,Administrator of the National Aero nautics and Space Administration,with respect to an invention of Clarence H. Heckler, Palo Alto, Calif.Filed Feb. 11, 1965, Ser. No. 432,030 4- Claims. (Cl. 321-48) ABSTRACTOF THE DISCLOSURE An interrupter consisting of a capillary tube, filledwith current-conducting liquid, such as mercury, with electrodes onopposite ends of the tube, for connecting the interrupter to associate-dcircuitry. When current flows between the electrodes through the liquid,the liquid tends to heat up, vaporizing at about the center of thecapillary tube, and thereby interrupting the flow of currenttherethrough. Upon the interruption of the flow of current, the NEIPOI,trapped within the tube between liquid sides, condenses back to liquidform to provide a subsequent continuous path for current flow. The rateof interruptions is a function of the properties of thecurrent-conducting liquid, the magnitude of the current and thedimensions of the capillary tube.

Origin of invention The invention described herein was made in theperformance of work under a NASA contract and is subject to theprovisions of section 305 of the National Aeronautics and Space Act of1958, Public Law 85568 (72 Stat. 435; 42 U.S.C. 4257).

This invention relates to an electrical interrupting circuit and, moreparticularly, to an improved electrical switching device utilizing acurrent-conducting liquid.

Various switching devices and techniques are employed to selectivelyenergize circuits or systems at selected rates, in order to controltheir manner of operation. Multicontact relays extensively used for suchpurposes, are but one example. By controlling the rate and manner atwhich the coil of a relay is energized, the flow of current throughdifferent ones of the multiple contacts is controlled. Similar devices,known as current interrupters or vibrators are used to convert directcurrent (DC) energy into alternating current (AC) energy for driving themany circuits which require A.C. energy for their operation.

In most prior art interrupting devices, the energy or current used tooperate the device usually is not the same as the current to beinterrupted. Again referring to a relay, the cur-rent used to drive thecoil is generally not the same current flowing through, or interruptedby the plurality of contacts which are closed or opened, as the case maybe, due to the energization of the coil of the relay. In a conventionalrelay, the current flowing through the contacts is completely unrelatedto the current supplied to the relays coil, thus requiring two ditferentcurrents for normal operation.

Accordingly, it is an object of the present invention to provide a noveland simplified current interrupting device.

Another object of the present invention is the provision of a simplifiedcurrent switching device, in which the current used to control theswitching operation of the device is the same as the current to beswitched thereby.

Another object of the present invention is to provide a novel currentinterrupting device utilizing a currentconducting liquid which is usedto control the interruption of the current, as well as conduct thecurrent therethrough between interruptions.

A futher object of the present invention is to provide a novel andsimple current interrupting device in which liquid mercury is utilizedas the current conducting medium for controlling as well as conductingthe current to be interrupted.

These and other objects of the present invention are achieved in anarrangement wherein a capillary tube is filled with a current-conductingliquid. The capillary tube connected in series with an appropriatecurrent load are connected across a source of electrical energy so thatcurrent flows through the electrical load as well as through thecurrent-conducting liquid in the capillary tube. The current flowingthrough the liquid affects its electrical, as well as, physicalcharacteristics. Consequently, the liquid par-ts at approximately themiddle of the capillary tube, thus interrupting the flow of currentthrough it, as well as, through the current load connected in seriestherewith.

When current flows through a current conducting liquid in a capillarytube, a constriction is provided near the middle of the tube, due to thepinch phenomena. This constriction increases the current density in theconstricted area which produces greater forces in a direction whichincreases the constriction and also produces localized Joule heating asthe constricted area has an increased resistance and a decreasedcapacity to conduct heat away from the area. As this process proceedsto- 1 ward an increasingly smaller cross sectional area, it

seems plausible that the Joule heating produces the break by vaporizingthe small thread of current-conducting liquid bridging the main bodiesof liquid. The are immediately following the break also produces some|vaporization. As the two bodies attempt to recombine the vapor has notcompletely condense-d, and when the re combination occurs this gas isentrapped, forming an area of reduced cross section and thushigher-current density. This point then has a higher force acting on itto.produce further constriction, and the cycle repeats, forming therupture again in the same area.

During the periods that the two bodies of liquid are recombined, currentflows through the liquid, as well as through the load connected inseries therewith. However, during the interruption periods, current doesnot flow to either. It is thus seen, that the current used to producethe interruption is the same current to be interrupted. Namely, a singlecurrent is used to perform both functions. The changes in the currentflowing through the load may be utilized to control a variety ofcircuits whose modes of operation are based on such current interruptionphenomena.

The novel features that are considered characteristic of this inventionare set forth with particularity in the ap pended claims. The inventionitself both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIGURE 1 is a schematic diagram useful in explaining the principles ofoperation of the current interrupter of the present invention;

FIGURE 2 is a simplified block diagram of one example of the applicationof the current interrupter of the present invention; and

FIGURE 3 is a simplified diagram of the second eX- ample of the use ofthe current interrupter of the present invention.

Reference is now made to FIGURE 1 wherein the current interrupter of thepresent invention designated 11 is shown connected in series with acurrent load 13 across a source of potential energy such as a battery15. The current interrupter 11 comprises a capillary tube 17 connectedbetween reservoirs 19 and 21, which are in turn connected via electrodes19E and 21E to the battery 15 and the current load 13 respectively. Thereservoirs 19 and 21 are substantially filled with a current-conductingliquid 22, so that the capillary tube connected at the bottom of the tworeservoirs is completely filled with such a liquid. The liquid may bemercury or any other liquid through which current may flow such assodium, gallium or potasslum.

As soon as the switch S1 is closed, current from the power sources 15flows through the current interrupter 11 as well as through the currentload 13. Such current tends to eifect the current conducting liquid inthe current interrupter 11, and in particular effects the liquid in thecapillary tube 17. As current continues to flow through the currentinterrupter, the liquid in the capillary tube 17 heats up as a functionof the value of current and resistive value thereof, until at some timea portion of the liquid at approximately the middle of the capillarytube is converted into a gaseous form. As a result, an interruption ofcurrent occurs between two liquid surfaces which are separated by agiven amount of gas trapped therebetween.

The interruption of current through the current interrupter 11, alsointerrupts the current flow through the current load 13 resulting in asudden drop of the current flowing therethrough. Once the current nolonger flows through the capillary tube 17, the gas trapped thereinbetween the two liquid surfaces quickly condenses back into liquid form,thereby providing a new continuous path for the current to flow throughthe capillary tube. As a result, current flows again through the currentinterrupter 11 as well as the current load 13, until due to the new flowof current a portion of the liquid is again converted into gaseous formand thereby again interrupts the current flow therethrough.

From the foregoing, it is thus seen that in the current interrupter ofthe present invention, the current used to produce the interruptions, isthe same on the current to be interrupted. Namely, the current suppliedfrom the source 15, initially produces the current interruptions in theinterrupter 11 by causing the liquid in the capillary tube to beconverted into gaseous form, which in turn causes the interruption ofthe current. Thus, an arrangement is provided wherein the current whichis being interrupted also produces the interruption elfect.

By properly controlling the maximum current which may flow in thearrangement shown in FIGURE 1, as well as controlling the dimensions ofthe capillary tube, and in particular the diameter thereof for a givencurrent conducting material a selected rate of interruption may beproduced. For example, in one actual reduction to practice, amercury-filled capillary tube 1 long and 0.010" in diameter was used tointerrupt current in excess of ampers at about 400 interruptions persecond, with the current waveform being essentially a square wave.

The novel and simple interrupter of the present invention mayconveniently be incorporated in any circuit where such currentinterruption is desired. For example, interconnecting it with a loadsuch as the load 13 (FIGURE 1) a selected current therethrough may beinterrupted at a predetermined rate. Similarly, the novel interrupter ofthe invention may be incorporated in a circuit for providing currentwhich alternates at a selected frequency.

Reference is now made to FIGURE 2 which is a simplified diagram of acircuit 25 for providing an alternating current (A.C.) signal from a DC.source 27. The circuit includes the interrupter 11 connected in serieswith a variable load 29 between the source 27 and the primary winding 31of a transformer 33, which is also connected to the source 27 through aswitch 35. The secondary windings 37 of the transformer 33 are connectedto a filter circuit 41, with the output thereof, designated by numeral43, providing the desired A.C. output signal.

From the foregoing description, it is apparent that after closing switch35 the DC. current from the source 27 is interrupted in the interrupter11, the rate of such phenomena depending on the dimensions of theinterrupter as well as the current flowing therethrough, and theparticular current-conducting liquid used thereon. Thus, by controllingthe variable resistor 29, it is possible to control the value of theuninterrupted current flowing through the interrupter 11 and therebycontrol the rate of interruption. Namely, the frequency of the varyingcurrent flowing through the primary 31 may be controlled.

As is known by those familiar with the art, the frequency of the varyingcurrent in the primary windings 31, is reflected in the frequency of thevarying current induced in the secondary windings 37 which, whenfiltered, may produce the sinusoidal A.C. signal 43. The frequency ofthe signal 43 is the same as the frequency of the varying current in theprimary windings 31. Thus, by merely varying the value of theuninterrupted current flowing through the interrupter 11, lead 29 andprimary windings 31, the frequency of the output signal may becontrolled. Varying such current is most conveniently accomplished bychanging the resistance of the load 29 which is in series with theinterrupter 11 and windings 31.

The novel interrupter of the invention, due to its simplicity ofoperation is similarly incomparable in circuits for producing singlepulses of predetermined characteristics rather than a continuouslyalternating signal, such as the AC. signal 43 (FIGURE 2). For example,the interrupter of the invention may be incorporated in a circuit forproducing single pulses, each of a predetermined time duration such asare produced by conventional one shot multivibrators.

Referring to FIGURE 3, there is shown a simplified diagram of anothermode of operation of the interrupter of the invention. As seen, theinterrupter 11 is connected in series with a variable resistor 47 and aresistor 49 across a DC source 51. A switch 53 is interposed between thesource 51 and interrupter 11. An electrical load 55 is connected througha resistor 57 to the junction point between element 47 and 49. From theforegoing, it is apparent that upon closing switch 53 current flowsthrough the interrupter 11 which, as a result, produces the interruptioneifect. The interruption of current occurs when some of the currentconducting liquid is vaporized, which is due at least in part to theheating of the liquid by the power losses. Current starts to flow againafter a portion of the vapor which is enclosed condenses again toprovide a complete path for current flow.

The rate of condensation of the vapor may be controlled by encasing theinterrupter Within a temperature controlled unit 59 so that thetemperature of the interrupter is controlled, thereby controlling thetime required for the vapor to condense to liquid form. As a result, thetime duration during which current does not flow is controlled, thuscontrolling the duration of a current signal 61 supplied through theresistor 57 to the load 55.

As long as the switch 53 is closed, the load 55 is supplied With a chainof signals, each of a duration controlled by the time required tovaporize the liquid and having an interval determined by the timerequired for the vapor in the interrupter 59 to condense to a liquidstate. It is apparent, however, that a single pulse may be supplied tothe load 55. This may easily be accomplished by causing the switch 53 toopen after the first interruption occurs. Thus, a single interruptionwill produce a single pulse. Thereafter, a second signal may be producedby closing switch 53 to produce a subsequent interruption which, uponoccurring, reopens the switch. Consequently, a single signal is producedeach time the switch 53 is closed. The minimum duration between pulsesis controlled by controlling the temperature of the interrupter, therebycontrolling the time required for the vapor to condense to a liquidstate.

Summarizing briefly, the novel current interrupter of the presentinvention comprises a capillary tube filled with a current conductingliquid through which current is caused to flow. As a result of thecurrent fiow, the liquid, in addition to various phenomena taking placetherein, heats up which vaporizes some of the liquid at about the centerof the tube. Consequently, the flow of current through the liquid isinterrupted. The current remains interrupted until the vapor condensesthereby again providing a current path through the liquid.

In such a novel arrangement, the current to be interrupted is used toalso produce the interruption phenomena. When using any given currentconducting liquid, the rate of interruptions as well as the duration ofeach interruption may be controlled by limiting the maximum currentflowing through the tube as well as controlling the dimensions of thecapillary tube and the temperature environment thereof.

The current interrupter may be incorporated in any switching or pulsingcircuit in a manner similar to other conventional more complicatedinterrupting circuits or devices.

There has accordingly been shown and described herein a novel and usefulapparatus for producing controlled current interruption. Modificationsand equivalents may be introduced in the arrangements as shown withoutdeparting from the true spirit of the invention. Therefore, all suchmodifications and equivalents are deemed to fall within the scope of theinvention as claimed in the appended claims.

What is claimed is:

1. A liquid current interrupter for interrupting at a selected rate theflow therethrough of current supplied thereto comprising acurrent-conducting liquid; a capillary tube filled with said currentconducting liquid; and means coupled to said capillary tube for causingcurrent to flow through said current-conducting liquid, and forinterrupting the flow of said current, the rate of interruptions beingat least a function of the properties of said current-conducting liquid,the magnitude of said current and the dimensions of said capillary tube.

2. A liquid current interrupter for interrupting at a selected rate theflow of current supplied thereto comprising a capillary column ofcurrent-conducting liquid; and means coupled to said capillary columnfor causing current to flow through said current-conducting liquid andfor gasifying some of said liquid to interrupt the flow of currenttherethrough, the rate of interruptions being at least a function of theproperties of said current-conducting liquid, the dimensions of saidcapillary column and the magnitude of said current.

3. A liquid current interrupter for interrupting at a selected rate theflow of current supplied thereto comprising a current conducting liquid;a capillary tube filled with said current conducting liquid; and meanscoupled to said capillary tube for causing said current to flow throughsaid current-conducting liquid, and for converting at least some of saidliquid to vapor so as to interrupt the flow of current therethrough,said vapor being contained Within said capillary tube between saidliquid, the rate of interruptions being a function of the properties ofsaid current conducting liquid, the magnitude of said current and thedimensions of said capillary tube.

4. A liquid current interrupter for interrupting at a selected rate theflow of current supplied thereto comprising a current conducting liquid;a capillary tube filled with said current conducting liquid; and meanscoupled to said capillary tube for supplying said current to flowthrough said current conducting liquid, for converting at least some ofsaid liquid to vapor to interrupt its flow therethrough until said vaporis condensed to liquid to thereby provide a subsequent continuous pathfor said current to flow therethrough.

References Cited UNITED STATES PATENTS 1,624,322 4/1927 EnglernanZOO-113.2 2,203,579 6/1940 Randolph 315-209 2,208,439 7/1940 Suits313-172 X 2,476,068 7/1949 Short 321-49 2,804,547 8/1957 Mortimer 321-44X JOHN F. COUCH, Primary Examiner. G. GOLDBERG, Assistant Examiner.

4. A LIQUID CURRENT INTERRUPTER FOR INTERRUPTING AT A SELECTED RATE THEFLOW OF CURRENT SUPPLIED THERETO COMPRISING A CURRENT CONDUCTING LIQUID;A CAPILLARY TUBE FILLED WITH SAID CURRENT CONDUCTING LIQUID; AND MEANSCOUPLED TO SAID CAPILLARY TUBE FOR SUPPLYING SAID CURRENT TO FLOWTHROUGH SAID CURRENT CONDUCTING LIQUID, FOR CONVERTING AT LEAST SOME OFSAID LIQUID TO VAPOR TO INTERRUPT ITS FLOW THEREBETWEEN UNITL SAID VAPORIS CONDENSED TO LIQUID TO THEREBY PROVIDE A SUBSEQUENT CONTINUOUS PATHFOR SAID CURRENT TO FLOW THERETHROUGH.